Sensorless Position Estimator for Reciprocating Linear Actuator Hardware

This Phase I project aims to demonstrate the effectiveness of a new sensorless piston position estimation technique for reciprocating linear actuators. During this six-month SBIR Phase I project, we propose constructing a model-based dynamic piston position observer in software and validating its performance using moving-coil linear actuator hardware. Our sensorless position estimator approach holds the potential to enhance the reliability and performance of NASA Radioisotope Power Systems (RPS) missions by supporting controllers that: 1) adjust the piston amplitude in response to radioisotope fuel decay or when individual redundant multi-converter units are activated or deactivated 2) identify and correct for piston mean position offset (“drift”) 3) coordinate the piston phase and amplitude of dual-opposed converters to minimize net vibration 4) manage single converter piston motion for optimal use of active/ passive vibration absorbers We understand that many of the convertor controllers developed by NASA already monitor coil current and terminal voltage. Therefore, controllers that contain microprocessors could, in principle, be upgraded to host our position estimation algorithms without requiring additional sensors or current injection hardware, thus enhancing overall system reliability. Furthermore, utilizing information about piston position (including amplitude, offset, and phase) could improve specific power density by allowing the controller to operate safely closer to the physical limits of piston travel while synchronizing with other converters and vibration absorbers. It may be feasible to implement our sensorless position observer for the linear actuator of an active (driven) vibration absorber, potentially eliminating the need for a separate accelerometer. Our piston position observer is suitable for moving-magnet-based converters and the low-power, low-inductance moving coil alternator-based converter developed by NASA-GRC.
Benefits: Our sensorless piston position estimator can support dynamic radioisotope power system (RPS) Stirling convertors at any power level – from tens of watts to kilowatts. According to the solicitation, NASA is considering using Stirling convertors “to power science missions for the Moon and other solar system bodies of interest… for use on space probes, landers, and rovers, battery chargers, sensors, etc.” We understand that many of the RPS convertor controllers developed by NASA already monitor coil current and terminal voltage. Therefore, controllers equipped with microprocessors could, in principle, be upgraded to host our position estimation algorithms without the need for additional sensors or current injection hardware, thereby enhancing overall system reliability, particularly during extended missions. Furthermore, utilizing information about piston position (including amplitude, offset, and phase) could improve specific power density by allowing the controller to operate more safely closer to the physical limits of piston travel while synchronizing with other converters and vibration absorbers. It might even be feasible to implement our sensorless position observer for the linear actuator of an active (driven) vibration absorber, potentially eliminating the need for a separate accelerometer. Our piston position observer is suitable for moving-magnet-based converters and the low-power, low-inductance moving coil alternator-based converter developed by NASA-GRC. Additionally, our position estimator could be utilized in NASA cryocooler applications to directly cool space sensors and reliquefy vapor for zero-boiloff fluid storage. The estimator could also apply to linear gas compressor/ liquid transfer pumps or other linear actuators applications. Our position estimator could support Stirling convertors for domestic micro-cogeneration appliances, portable power and battery charging systems, and terrestrial remote power applications requiring high reliability (e.g., navigation or communications equipment at off-grid sites). Our estimator IP could also provide sensorless piston position feedback capability to cryocooler controllers, enhancing performance and reliability. The global market for Stirling cryocoolers is expected to reach $7.4 billion (USD) by 2026, with a compound annual growth rate of 10.5% from 2021 to 2026. In the U.S., the Stirling cryocooler segment is projected to experience the highest growth rate among all cryocooling technologies during the forecast period 2022-2030. Through the I-Corps interviews from our last SBIR project, we identified the potential relevance of our sensorless position estimation IP for industrial actuators, including solenoids and valves, closed-loop control of moving-coil speakers, and active automotive suspensions.